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Guide to Handling Next.js Unhandled Promise Rejection Errors

Anchal Rastogi
~ 4 min read | Published on Feb 28, 2024





TABLE OF CONTENT

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Introduction

Unhandled Promise Rejection Errors in Next.js can be a significant source of frustration for developers, leading to unexpected behavior and application crashes. In this guide, we'll explore these errors in depth and provide effective strategies to handle and prevent them.

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Understanding Unhandled Promise Rejection Errors in Next.js

Unhandled Promise Rejection Errors occur when a Promise is rejected but no error handler is provided to catch the rejection. In Next.js applications, this can happen when asynchronous operations, such as API requests or file system operations, fail unexpectedly.

Scenario 1

Error code

const fetchData = async () => {
  const response = await fetch('<https://api.example.com/data>');
  const data = await response.json();
  throw new Error('Data retrieval failed');
};

fetchData();

Corrected code

const fetchData = async () => {
  try {
    const response = await fetch('<https://api.example.com/data>');
    const data = await response.json();
    return data;
  } catch (error) {
    console.error('Error fetching data:', error);
    throw error;
  }
};

fetchData().catch(error => console.error('Unhandled promise rejection:', error));

Solution Summary

In this scenario, the error occurs due to the lack of error handling in the asynchronous fetchData function. By adding a try-catch block and properly handling the error, we prevent the unhandled promise rejection error.

Scenario 2

Error code

const fetchUserData = async () => {
  const response = await fetch('<https://api.example.com/user>');
  const userData = await response.json();
  return userData;
};

fetchUserData().then(userData => console.log(userData.name));

Corrected code

const fetchUserData = async () => {
  try {
    const response = await fetch('<https://api.example.com/user>');
    const userData = await response.json();
    return userData;
  } catch (error) {
    console.error('Error fetching user data:', error);
    throw error;
  }
};

fetchUserData()
  .then(userData => console.log(userData.name))
  .catch(error => console.error('Unhandled promise rejection:', error));

Solution Summary

Here, the error occurs because the Promise returned by fetchUserData is not properly handled. By adding a catch block to handle any potential errors, we prevent the unhandled promise rejection.

Scenario 3

Error code

const fetchData = async () => {
  const response = await fetch('<https://api.example.com/data>');
  const data = await response.json();
  return data;
};

fetchData().catch(error => console.error('Unhandled promise rejection:', error));

Corrected code

const fetchData = async () => {
  try {
    const response = await fetch('<https://api.example.com/data>');
    const data = await response.json();
    return data;
  } catch (error) {
    console.error('Error fetching data:', error);
    throw error;
  }
};

fetchData().catch(error => console.error('Unhandled promise rejection:', error));

Solution Summary

In this scenario, the error occurs due to the lack of error handling in the fetchData function. By adding a try-catch block and properly handling the error, we prevent the unhandled promise rejection.

Handling Unhandled Promise Rejection Errors in Next.js

To handle Unhandled Promise Rejection Errors effectively:

  • Always add a catch block to asynchronous functions to handle any potential errors.
  • Use try-catch blocks within asynchronous functions to catch and handle errors locally.
  • Ensure that Promises are properly handled using either catch blocks or try-catch-finally constructs.

Proactive Error Debugging with Zipy

For proactive error monitoring and debugging in Next.js applications, consider using Zipy. Zipy provides advanced error monitoring and session replay capabilities, allowing developers to identify and resolve Unhandled Promise Rejection Errors efficiently, ensuring a seamless user experience.

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Conclusion

Unhandled Promise Rejection Errors in Next.js can be mitigated by implementing proper error handling strategies and ensuring that Promises are handled appropriately. By following best practices and utilizing tools like Zipy, developers can effectively debug and prevent these errors, ensuring the reliability and stability of their applications.

Resources on how to debug and fix Next.js errors

Frequently Asked Questions

Q: What are Unhandled Promise Rejection Errors in Next.js? A: Unhandled Promise Rejection Errors occur when a Promise is rejected but no error handler is provided to catch the rejection, leading to unexpected behavior in Next.js applications.

Q: How can I prevent Unhandled Promise Rejection Errors in my Next.js application? A: To prevent Unhandled Promise Rejection Errors, always add a catch block to asynchronous functions and ensure that Promises are properly handled using try-catch blocks or catch methods.

Q: Why is proper error handling important in asynchronous code? A: Proper error handling is crucial in asynchronous code to catch and handle errors that may occur during asynchronous operations, preventing unhandled promise rejections and ensuring robustness in the application.

Q: Can I use Zipy to debug Unhandled Promise Rejection Errors in my Next.js application? A: Yes, Zipy offers proactive error monitoring and debugging capabilities for Next.js applications, allowing developers to identify and resolve Unhandled Promise Rejection Errors efficiently.

Q: How does Zipy help in debugging Unhandled Promise Rejection Errors? A: Zipy provides advanced error monitoring and session replay capabilities, enabling developers to pinpoint Unhandled Promise Rejection Errors, understand their root causes, and resolve them effectively, ensuring a seamless user experience.

Key Takeaways

  • Always add a catch block to asynchronous functions to handle any potential errors and prevent unhandled promise rejections.
  • Use try-catch blocks within asynchronous functions to catch and handle errors locally, ensuring robust error handling.
  • Properly handle Promises using catch blocks or try-catch-finally constructs to prevent unexpected errors in Next.js applications.
  • Utilize tools like Zipy for proactive error monitoring and debugging to identify and resolve Unhandled Promise Rejection Errors efficiently.

Call to Action

Feel free to comment or write to us in case you have any further questions at support@zipy.ai. We would be happy to help you. In case you want to explore for your app, you can sign up or book a demo.











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